From pockets to plungers – a sampling valve update

Sampling valves may look like simple items of equipment, but a lot of thought can be required to select the right valve for each application.

About the author

David Sear is Online Editor. He is contributing to articles, interviews and reports to KCI’s magazines and websites. David also works on videos for KCI Television.

I’ll never forget that sense of confusion I experienced when, visiting one of my first trade shows, I was handed a small bore ball valve that had a major flaw. The item in my hands looked like a ball valve all right, but for some inexplicable reason the manufacturer had only drilled out half of the necessary orifice through the ball!

The stand-holder stood looking at me with amusement in his eyes. “Never seen one before, eh? Well, it’s actually a sampling valve. It can be connected to a branch off a pipeline, or to a vessel, etc, and it allows you to safely withdraw a pre-determined volume of fluid from whatever is inside the process. Such samples might be needed for quality control, testing, or regulatory compliance, etc.”

With his clear explanation the penny immediately dropped as to how this particular sampling valve – which he referred to as a pocket design – worked. He then went on to quickly show me some alternative designs which all seemed equally logical and straightforward. However, I then made the second mistake of the day by assuming that selecting a sampling valve would be quite an easy process.

“Oh no, there are a great many issues to consider – possibly even more than when selecting a standard valve,” was his reply. He then went on to list topics that had to be borne in mind. Many seemed obvious, such as of course the pressure and temperature of the medium, whether it was corrosive or not, the dangers associated with hazardous media, etc. However, there were a couple of unexpected additional factors, such as whether the medium, once withdrawn from the process, might start to solidify and block the valve, hence preventing further use. And the need to avoid dead spaces in the valve, where material might accumulate and similarly prevent the valve from operating properly.

In short, this meeting proved to be a highly instructional half-hour and I went away assuming that sampling valves would be a regular feature of my career here at Valve World. But for some reason or another not that many items seem to have reached us about sampling systems during my time here. And that’s a pity, because I am sure there is plenty to say about the design, application and maintenance of sampling valves.

So I was highly delighted to receive a technical paper covering plunger valves earlier this month, which will definitely be included in an upcoming issue of Valve World magazine. Also noteworthy is that the authors are employed by an EPC so have been able to provide an independent viewpoint when discussing points to consider in the plunger design.

But of course we are open to information on sampling valves from other sources. So if you are a manufacturer, distributor, user, etc, of sampling valves, then I’d be delighted to hear what you have to say. As always, the address is: d.sear@kci-world.com